Water is often used as a bulk fluid to transport various chemicals which are intended to be used in a dilution ratio. Since it is often inconvenient or expensive to transport and store chemical solutions at their intended working concentrations, various methods have been devolved to mix concentrated chemicals into a flow stream of other fluids. Metering pumps, batch tanks, spraying of concentrated chemicals are all typical methods currently in use today. Feeding chemicals by using a venturi is also very common.
In this chemical dilution, mixing and delivery method, a particular orifice is chosen to create a low-pressure region. In this low-pressure region, a port is adapted to allow another feed of fluid to be drawn into the main flow stream. It is under this low pressure that concentrated chemicals can be metered in using a partial vacuum. As long as there is a suitable difference in the inlet and outlet pressures, these venturi-based chemical delivery systems are simple, reliable and work very well.
Currently in the marketplace, similar eductors/injectors are hard plumbed or directly threaded into manifold blocks using traditional National Pipe Thread Tapered Thread (NPT) threads. This can be difficult to deal with in the field when additional plumbing or piping is attached or the injector arrangement is reconfigured. Typical eductors have an operational life of 1-3 years at which point they typically need to be replaced.
Pipe threads are commonly understood to be a permanent method of connecting pipe sections and fittings. While it is possible to remove a pipe thread joint and reassemble it, it generally requires tools and significant maintenance time. Depending upon the fluids and operational environments, oftentimes the mating threads will deteriorate with use. Also, pipe thread connections can be prone to leaking unless large forces are used to tighten and eliminate any gaps. In many instances, connection sealants such as Teflon tape can be used to seal pipe thread connections but this method can facilitate very high hoop-stresses in the pipe fittings, which can result in splitting within the metal or plastic fittings during assembly or alternatively, lead to fatigue cracking over time. The reason this is common is that Teflon is a very friction-free material and will allow much higher hoop-stress to be attained relative to torque. Also, Teflon tape builds thickness and can add to the effective diameter leading to additional hoop-stress. Finally, the use of Teflon tape or can result in fouling of precision orifices, valves and other critical components by the release of small shards of debris. While other conventional thread sealants may overcome many of the disadvantages of using Teflon tape with pipe threads, these pastes and liquids can be messy and tend to harden over time which can make joint disassembly almost impossible.
While the aforementioned difficulties of conventional pipe and tubing connections can lead to increased expense in maintaining conventional piping arrangements, these difficulties are even more pronounced within chemical injection systems that utilize a manifold to inject a plurality of distinct chemicals into a fluid stream.